Folded-spiral EDWAs with continuously varying curvature

The layout of folded spiral erbium-doped planar waveguide optical amplifiers (EDWAs) is considered. A quasi-continuous function to describe the curvature of a folded-spiral layout is presented, based upon the use of cosine and raised-cosine variations in bend curvature. This layout provides greater gain in a given area than the corresponding fixed-radii layout. Analysis is initially based on simple geometric principles and the reduction of bending losses for 180° waveguide bends. Fold-back bends and complete EDWA layouts are then considered. Simulations are carried out using an algorithm that combines five-level rate equations with propagation by the method of lines.